This proposal examines type A and B complexes of peptide-MHC class II molecules and their corresponding unique T cells. Type A and B pMHCs represent different conformational isomers, generated in different intracellular compartments of the antigen presenting cell (APC): type B pMHC are generated in endocytic vesicles different from the pMHC assembly - or MIIC - compartment. In the case of lysozyme (HEL), the explanation centers on the editing role of H-2DM. The proposal contains two major goals described in overlapping sections. Experiments using type B T cell receptor (TCR) transgenic mice indicate that in vivo, the T cells were activated by HEL administered with inflammatory agents or adjuvants. In vivo and ex vivo experiments will follow the paths that the protein HEL takes in order to generate the type B epitopes, i.e. peptide release, release via exosomes, change in intracellular traffic, and presentation by way of apoptotic material. In vivo experiments include intra-vital microscopy in order to trace the dynamics of antigen presentation of type B (and A) T cells: the type B T cell, because of its uniqueness in being presented in a non-DM site, serves as an indicator of how antigen presentation and T cell stimulation may develop and spread beyond the first cell that takes up the antigen. We propose examining the potential of a type B T cell to induce pathology by using the TCR transgenic mouse genetically crossed to mouse strains that express HEL. Type B T cells directed to an autologous protein evade negative selection: a scenario is envisioned whereby peptides from an autologous tissue protein are released and activate the dormant type B T cells and cause pathology. Strains expressing HEL expressed on beta cells will allow us to examine the pathological potential of the type B T cells, and the conditions that may lead to diabetes development. Finally, the possibilities are considered that type B T cells could have other functional expressions depending on the continuous and systemic release of peptides from HEL. We will examine the MLA11.2 TCR transgenic mice when bred into strains in which HEL is expressed systemically, either in the circulation or in the APC network. Importantly, abundant type B T cells to insulin were found spontaneously in the NOD mouse. This seminal finding may be part of the explanation for the development of diabetic autoimmunity. T cells will be examined for the nature of recognition of insulin epitopes. We will examine presentation of insulin at both a biochemical and functional level, searching for the natural peptides bound to I-Ag7 molecules, as well as peptides in the beta cell granule that may explain the development of type B pMHC complex. We will examine the interactions of insulin and insulin peptides with H2-DM and I-Ag7. The biological role of the type B T cells to insulin peptides will be examined under various situations, focusing in particular on their diabetogenic potential. PROJECT NARRATIVE: This investigation examines the function of a set of T cells that participate in autoimmune reactions. It examines how these T cells are activated. It contains a section examining these T cells in diabetic autoimmunity, i.e. type 1 diabetes mellitus.